Logo not showing up all the time

I’ve added a logo to my website (using the tiny forge theme). It displays without any problem.

I noticed however that the logo is not showing up on my mobile device. I’ve noticed the same problem when I scale down the size of the browser window on my PC. The logo keeps disappearing and popping up again.

normal view (with logo) : https://tinypic.com/r/nef5mh/8
smaller window/mobile view (no logo) : https://tinypic.com/r/wtce86/8

Thanks a lot for any reply !